The present invention relates generally to a clothes washing machine having an electronically controlled motor and, more particularly, to such a machine for advantageously utilizing heat resulting from motor control circuit losses, which would otherwise be wasted energy.
There have been a number of proposals to eliminate the mechanical transmission conventional in clothes washing machines for converting relatively high speed unidirectional motor rotation to low speed oscillatory (reversing) motion for agitation. These proposals envision coupling of a reversible, speed controllable DC motor either directly or through simple reduction gearing to the washing machine agitator. Through suitable control of the motor winding energization, desired agitator motion can be effected.
A number of suitable DC motor control circuits have been proposed employing various forms of semiconductor switching elements for effecting the desired control of motor rotational velocity and direction. By way of example, without in any way intending to limit the scope of the invention, such semiconductor switching elements include power bi-polar transistors, power field effect transistors, silicon controlled rectifiers (SCR's), triacs, and other forms of thyristors. Additionally, many such circuits employ free-wheeling diodes. Examples of such circuits may be found in the following U.S. Patents: Elliott et al U.S. Pat. No. 3,152,462; Sones et al U.S. Pat. No. 3,152,463; Crane et al U.S. Pat. No. 3,369,381; and Lake U.S. Pat. No. 3,503,228. Further examples may be found in the following commonly-assigned U.S. patent applications: Ser. No. 109,587 filed Jan. 4, 1980, by Robert P. Alley Ser. No. 109,579, filed Jan. 4, 1980, by Robert P. Alley and Richard C. Weischedel; and Ser. No. 109,705, filed Jan. 4, 1980, by John F. Park.
In such circuits, the semiconductor motor control elements are generally operated in a high efficiency switching mode such that minimal losses occur in the semiconductor switching elements. However, due to the substantial power switching requirements to control up to a horsepower DC motor with directional reversals more than once per second, substantial circuit losses, particularly in the switching transistors, nevertheless occur. These circuit losses are in the order of 25 to 70 watts.
As is known, such heating of power semiconductors results in a temperature rise which would rapidly destroy the semiconductors if not somehow dissipated. For this reason, heat sinks are conventionally provided for power semiconductors to carry away this excess heat.